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PubMed1986

Effect of partition walls and neighboring buildings on the indoor exposure rate due to cosmic-ray muons.

Numerical calculations were done of the indoor exposure rate due to the cosmic rays. Only muons were considered, and the calculations were done within a two-dimensional framework under the non-scattering approximation. The effects of various structural parameters on the level and the distribution of the exposure rate were studied by a case control method. It was shown that a building's dimensions and the floor thickness were important in all cases. However, the effect of partition walls would become significant only when the partition number is large. The effect of neighboring buildings would be especially important in the lower floors of tall buildings. In such a case, attention is necessary not only to the buildings' internal structures but also to the relationship between that particular building and its neighborhood. The maximum amplitude of the possible variation of the exposure rate due to the change of any single structural parameter would be 30% in ordinary Japanese housing conditions.

Building Codes↗
PubMed1987

Altitude variation of cosmic-ray neutrons.

The altitude variation of the cosmic-ray neutron energy spectrum and the dose equivalent rate was measured at an average geomagnetic latitude of 24 degrees N by using the high-efficiency multi-sphere neutron spectrometer and neutron dose-equivalent counter developed by the authors. The data were obtained from a 2-h flight over Japan on 27 February 1985. The neutron energy spectra measured at sea level and at altitudes of 4,880 m and at 11,280 m were compared with the calculated spectra of O'Brien and with other experimental spectra, and they are in moderately good agreement with them. The dose equivalent rate increases according to a quadratic curve up to about 6,000 m and then increases linearly between 6,000 m and 11,280 m. The dependence of dose equivalent rates at sea level and at an altitude of 12,500 m on geomagnetic latitude also is given by referring to other experimental results.

Altitude↗
PubMed1988

An evaluation of energy-independent heavy ion transport coefficient approximations.

Using a one-dimensional transport theory for laboratory heavy ion propagation, evaluations of typical energy-independent transport coefficient approximations are made by comparing theoretical depth-dose predictions to published experimental values for incident 670 MeV/nucleon 20Ne beams in water. Results are presented for cases where the input nuclear absorption cross sections, or input fragmentation parameters, or both, are fixed.

Cosmic Radiation↗
PubMed1998

Residual 60Co activity in steel samples exposed to the Hiroshima atomic-bomb neutrons.

Residual 60Co radioactivity produced by the neutrons from the Hiroshima atomic bomb has been measured by means of gamma-ray spectrometry for seven steel samples located up to 1,800 m slant range and one control sample obtained at 4.5 km from the hypocenter. After removing the main constituent of iron ions from the steel sample by the solvent extraction method, nickel and cobalt were chemically separated by the ion exchange process. Gamma-ray measurements were performed with a low background well-type germanium detector. Derived specific activities 60Co:Co were compared with previous measurements and with the calculation based on the neutron fluence of current dosimetry system DS86. It has been shown that a systematic discrepancy exists between the measured and calculated activity. The calculated-to-measured ratios for 60Co are consistent with those of 152Eu and 36Cl activity.

Chlorine↗
PubMed2003

Cosmic-ray-induced neutron spectra and effective dose rates near air/ground and air/water interfaces in Taiwan.

The ground-level cosmic-ray neutrons were measured at various elevations from sea level to 4,000 m in Taiwan, where the vertical cutoff of geomagnetic rigidity is high. High-efficiency Bonner cylinders were used in the measurements. The measured results were used to normalize and confirm one-dimensional transport calculations for cosmic-ray neutrons near interfaces. According to these measurements and calculations, the ground-level neutron fluence rates, effective dose rates, and their altitude dependence in Taiwan were determined. As compared with that reported elsewhere, the appreciable differences both in their absolute values and associated dependence on altitude could be attributed to the substantial latitude effect. In addition, the energy spectra of cosmic-ray neutrons near air/ground and air/water interfaces were measured. The neutron fluence rate near the air/ground interface is greater than that near the air/water interface; however, the spectral shape is harder at the air/water interface than at the air/ground interface. The air/ground and in-flight spectra differ somewhat at low energies, especially in the thermal energy region, but the general shapes of the spectra are similar to each other. The influence of the difference in spectral shape on the evaluation of effective dose rate was investigated.

Air↗
PubMed2002

Neutrino oscillations.

The wave theory of light, and in particular the principle of interference, was formulated by Thomas Young in 1801. In the 20th century, the principle of interference was extended to the quantum mechanical wave functions describing matter. The phenomenon of quantum mechanical interference of different neutrino states, neutrino oscillations, has provided one of the most exciting developments in high energy particle physics of the last decade. Observations of the flavour oscillations of neutrinos produced by distant sources, such as from the core of the Sun, provide compelling evidence that neutrinos have mass. This article describes the main features and the most significant experimental observations of this unusual application of the principle of interference.

Atmosphere↗
PubMed2005

Cosmology with weak lensing surveys.

Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bi-spectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy.

Astronomy↗
PubMed1986

Theoretical antideuteron-nucleus absorptive cross sections.

Antideuteron-nucleus absorptive cross sections for intermediate to high energies are calculated using an ion-ion optical model. Good agreement with experiment (within 15 percent) is obtained in this same model for mean p-nucleus cross sections at laboratory energies up to 15 GeV. We describe a technique for estimating antinucleus-nucleus cross sections from N mean N data and suggest that further cosmic ray studies to search for antideuterons and other antinuclei be undertaken.

Cosmic Radiation↗
PubMed1986

Quantum mechanical signature in exclusive coherent pion production.

We calculate the coherent production of pions from subthreshold to relativistic energies in heavy-ion collisions using a quantum, microscopic, many-body model. For the first time, in this approach, we use harmonic oscillator wave functions to describe shell-model information. The theoretical quantum mechanical results obtained for the pion spectra represent an important improvement over our previous microscopic, many-body calculations.

Cosmic Radiation↗
PubMed1989

Fragmentation cross sections of 28Si at 14.5 GeV/nucleon.

We used CR39 plastic nuclear track detectors (C12H18O7) in combination with automatic track measurement techniques to determine total charge changing and partial cross sections for the production of fragments of charge ZF = 6 to ZF = 13 in collisions of 28Si beam nuclei at 14.5 GeV/nucleon in targets H, C, CR39, (C18H38O), Al, Cu, Ag, and Pb. By application of factorization rules, measured partial cross sections are separated into pure nuclear and electromagnetic components. The cross sections for electromagnetic dissociation agree with theoretical models. The results are consistent with a Z2 dependence of virtual photon spectra.

Cosmic Radiation↗